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Abstract:

There is provided a binocular device, including a rigid mechanical body
supporting two image sources (2, 4), one for each eye (6, 8) and two
lensing devices (12, 14), one for each eye, the lensing devices having a
first surface adjacent to the image sources and an opposite, second
surface, each of the lensing devices projecting an image (16, 18) of one
image source onto an infinite focal plane, and electronic means
permitting modification of an image generated to an eye for adjusting the
binocular alignment of the images. A method for aligning a binocular
device is also provided.

Claims:

1. A binocular device, comprising:a rigid mechanical body supporting two
image sources, one for each eye and two lensing devices, one for each
eye;said lensing devices having a first surface adjacent to the image
sources and an opposite, second surface;each of said lensing devices
projecting an image of one image source onto an infinite focal plane,
andelectronic means permitting modification of at least one image
generated to an eye for adjusting the binocular alignment of said images.

2. The binocular device of claim 1, wherein said electronic means for
modifying an image comprises a clock-stream delay line capable of
shifting pixels of the image in two dimensions to a programmed value.

3. The binocular device of claim 1, wherein said electronic means for
modifying an image comprises a double buffer feeding a processor.

4. The binocular device of claim 1, wherein the image sources provide
control over lateral shifts of the image.

5. The binocular device of claim 1, wherein said electronic means for
modifying an image is capable of generating dark pixels where a modified
image is inactive.

6. The binocular device of claim 1, further comprising two combiners, each
disposed adjacent to said second surface of the lensing device.

7. The binocular device of claim 1, further comprising two LOE-based
combiners, each disposed adjacent to said second surface of a lensing
device.

8. The binocular device of claim 5, wherein said two LOE-based combiners
are operative to cover a range of IPD values.

9. The binocular device as claimed in claim 1, wherein said body comprises
mechanical means for loosely holding alignment components in the device
to be cemented in place after binocular alignment.

10. The binocular device as claimed in claim 1, wherein said body
comprises sufficiently accurate mechanical means for binocular alignment
to within the coarse tolerance, such that only electronic alignment is
required to achieve fine binocular alignment.

13. The binocular device as claimed in claim 6, further comprising an
eyeglasses frame, wherein each of said image source and lensing devices
is affixed to portions of the frame.

14. The binocular device as claimed in claim 13, wherein each of said
image source and lensing optics is mounted in two independent enclosures
and wherein binocular alignment is affected by tilting at least one of
said independent enclosures.

15. The binocular device as claimed in claim 6, further comprising a
wearable fixture, wherein each of said lensing devices and image sources
are mounted onto each combiner, and a coarse alignment means is provided
to tilt the combiner-lensing-source assembly.

16. The binocular device as claimed in claim 15, wherein the wearable
fixture is an eyeglasses frame.

17. The binocular device as claimed in claim 6, further comprising a
wearable fixture, wherein each of said lensing devices is mounted onto
each combiner, and coarse alignment means is provided to move the at
least one of the image sources.

18. An alignment monitoring apparatus for a binocular device of claim 1,
comprising an optical folding device for diverting at least one image
into an auto collimator.

19. An alignment monitoring apparatus as claimed in claim 18, wherein said
optical folding device is an LOE.

20. An alignment monitoring apparatus as claimed in claim 18, comprising
an autocollimator for collecting light beams from both of the binocular
image sources.

21. The alignment monitoring apparatus as claimed in claim 20, further
comprising a camera for receiving light beams from the autocollimator and
transforming the beams into signals to be fed to a processor.

22. The alignment monitoring apparatus as claimed in claim 18, wherein
said electronic means is monitored by a processor capable of controlling
the alignment of the line-of-site of each image.

23. The binocular device as claimed in claim 1, wherein said lensing
devices are magnifying lenses.

24. The alignment monitoring apparatus as claimed in claim 18, wherein the
image pattern of each image source is the pixel structure of the image
source.

26. A method for aligning a binocular device according to claim 1,
comprising:generating an image pattern on each of the image
sources;mechanically aligning at least one of said image sources with the
image pattern overlapping each other, andelectronically further aligning
the overlap between said image patterns.

27. The method as claimed in claim 26, wherein said lensing devices are
magnifying lenses and the method further comprising the step of
magnifying the image patterns before alignment.

28. The method as claimed in claim 26, wherein said electronic alignment
is effected by modifying at least one of said image patterns in at least
one dimension for achieving a precise overlap between image pixels of the
two images.

Description:

FIELD OF THE INVENTION

[0001]The present invention relates to binocular optical systems, and in
particular, to binocular devices and methods of alignment thereof.

[0002]The invention can be implemented to advantage in binocular personal
display applications, including two-dimensional and three-dimensional
views with or without see-through capabilities. The word "binocular" as
used herein refers to an optical device suitable for viewing with two
eyes. The more common use of "binocular" as short-hand for "binocular
telescope" is referred to herein as "Binoculars".

BACKGROUND OF THE INVENTION

[0003]Personal displays are growing in importance with increasing
proliferation of mobile and wearable communication, information and
entertainment devices, in addition to their more traditional applications
for simulators, mixed reality and other head-mounted applications. In
many situations a binocular personal display system is preferred to a
monocular personal display system for its superior convenience of use
over protracted periods. Nevertheless, a binocular personal display
requires stringent alignment of the lines-of-sight of the two displayed
images. Relatively small misalignment can lead to serious user
discomfort, headaches, nausea, and, in extreme cases, symptoms of
sea-sickness and other ailments. In general, binocular alignment,
requires careful design of the binocular device and often involves
alignment procedures. The line-of-sight of the two eyes must be adjusted
to lie in the same horizontal plane, bisecting both eyes through their
centers, to an accuracy of a few minutes of an arc. Within this
horizontal plane the lines-of-sight should be adjusted to cross at the
region of the apparent distance of the observed object (this horizontal
offset between the lines-of-sight is termed parallax). Both of these
angular alignments must be maintained for different inter-pupil distance
(IPD) of the user. The IPD of the population typically varies between 54
and 75 mm. A mechanical adjustment for the distance between the pupils is
required to ensure a correct IPD, such as is well-known in common Porro
Prism Binoculars. Suitable mechanisms for aligning and maintaining the
binocular alignment over different IPDs are relatively large and
incompatible with personal displays, which are required to be compact.

[0004]Many different methods have been devised for binocular alignment,
however, so far, some proposed solutions require elaborate alignment
methods, while others incorporate mechanical fixtures and alignment
mechanisms, which significantly enlarge the personal display devices. The
trade-off between the interest to reduce the size and weight of personal
displays and the need for accurate binocular alignment is challenging and
has resulted in many personal displays that are insufficiently aligned,
and others that are inconveniently bulky.

DISCLOSURE OF THE INVENTION

[0005]It is an object of the present invention to provide a personal
binocular device with high alignment accuracy, while maintaining a
compact structure.

[0006]It is a further object of the present invention to provide a method
of aligning a binocular device first mechanically and then further
aligning it electronically.

[0007]In accordance with the invention there is therefore provided a
binocular device comprising a rigid mechanical body supporting two image
sources, one for each eye and two lensing devices, one for each eye, said
lensing devices having a first surface adjacent to the image sources and
an opposite, second surface, each of said lensing devices projecting an
image of one image source onto an infinite focal plane, and electronic
means permitting modification of at least one image generated to an eye
for adjusting the binocular alignment of said images.

[0008]The invention further provides a method for aligning a binocular
device comprising a rigid mechanical body supporting two image sources,
one for each eye and two lensing devices, one for each eye, said lensing
devices having a first surface adjacent to the image sources and an
opposite, second surface, each of said lensing devices projecting an
image of one image source onto an infinite focal plane, and electronic
means permitting modification of at least one image generated to an eye
for adjusting the binocular alignment of said images; generating an image
pattern on each of the image sources, mechanically aligning at least one
of said image sources with the image pattern overlapping each other, and
electronically further aligning the overlap between said image patterns.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]The invention is described in connection with certain preferred
embodiments, with reference to the following illustrative figures so that
it may be more fully understood.

[0010]With specific reference to the figures in detail, it is stressed
that the particulars shown are by way of example and for purposes of
illustrative discussion of the preferred embodiments of the present
invention only, and are presented in the cause of providing what is
believed to be the most useful and readily understood description of the
principles and conceptual aspects of the invention. In this regard, no
attempt is made to show structural details of the invention in more
detail than is necessary for a fundamental understanding of the
invention. The description taken with the drawings are to serve as
direction to those skilled in the art as to how the several forms of the
invention may be embodied in practice.

[0015]FIG. 4 is a block diagram illustrating a double-buffer scheme for
modifying an image to affect the required alignment control in accordance
with the present invention;

[0016]FIGS. 5A to 5D schematically illustrate four arrangements for
monitoring the alignment of a binocular personal display;

[0017]FIGS. 6A to 6C schematically illustrate three arrangements for
implementing folding optics for use with an alignment device for
binocular alignment of a binocular, according to the present invention;

[0018]FIGS. 7A and 7B illustrate perspective views of two embodiments of a
binocular device according to the present invention, including combiners;

[0019]FIG. 8 is a perspective view of an embodiment of the device
according to the present invention in the form of eyeglasses, and

[0020]FIG. 9 illustrates an embodiment of an image source mount including
a focusing mechanism, according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021]FIG. 1 schematically illustrates a typical binocular personal
device, including two image sources 2, 4, one for the left eye 6, and one
of the right eye 8 of an observer, mounted on a rigid mechanical body 10.
Two magnifying lensing devices 12, 14, are also mounted onto the same
mechanical body 10, one for magnifying the left image source 2, and one
for magnifying the right image source 4. The lensing devices 12, 14 may
be embodied by common lenses, reflection lenses, diffractive optics such
as holograms, combinations thereof, or any other image magnifying
devices, with or without folding optics for compressing its size. The
lensing devices generate two virtual images, 16 and 18 to be viewed,
respectively, by the left eye 6 and the right eye 8. The coordinate
system, illustrated in the right hand side of the figure, defines the
axes as follows: the linear axes Z in the direction of the line-of-sight
to the image, and X and Y in the lateral directions. The rotational axes
θ, a rotation about the Y-axis, φ a rotation about the Z-axis
and φ about the X-axis. The two virtual images 16, 18 should be
aligned to the binocular alignment tolerance. This is typically defined
as alignment of the two lines-of-sights from each eye to its virtual
image to lie in the X-Z plane, and to cross each other in the region of
the focal plane of the images. There is also a requirement that the two
images be oriented without relative rotation in the X-Y plane. In
general, to meet these requirements, the personal display must be
adjusted to the IPD of the user, and then determine the lines-of-sight of
both eyes, so as to binocularly align them.

[0022]The present invention significantly simplifies the binocular
alignment process. First, the personal display system is designed to
present the images at infinity. At this focal distance, binocular
alignment requires that the two lines-of-sight be parallel, a relatively
straightforward geometry to define and align to. Furthermore in this
configuration all the image components are essentially plane waves and
there is no variation of the image as the observer's eyes move across the
input aperture of each displayed image. In other words, in contrast to
more general arrangements with different focal depths, there is no
correction necessary for any deviation of the viewer's eyes from the
optical axes of the two images. The present invention therefore offers
two significant advantages: the binocular alignment of the proposed
device is entirely independent of the location of the eye, and it does
not depend on image content. This permits the calibration of the device
in the factory and its application with no need for additional parallax
corrections.

[0023]The further advantage of the present invention resides in a method
to facilitate and simplify the binocular alignment itself. For this
purpose use is made of the characteristics of a lens imaging to infinity
in transforming lateral position on the image source to output angle.

[0024]FIG. 2 illustrates a lens 12 with an image source 2 at its focal
point generating a virtual image at infinity. It is well known that for
this arrangement each pixel of the image source is transformed into
essentially a plane wave, each image pixel generating such a plane wave
traveling in a different direction. The pixel at the center of the image
generates a wave traveling along the optical axis of the lens, pixel `a`
generating a wave A. The further away the pixel is from the center of the
image, the larger the angular offset of the resulting wave from the
optical axis of the lens; pixels `b` and `c` generating waves B and C,
respectively. The present invention makes use of this lens characteristic
to adjust the direction of the line-of-sight of the image generated as
will be described below.

[0025]Good binocular performance requires the alignment of the
lines-of-sights of the two images to within a few minutes of arc. This is
typically a challenging requirement for a mechanical arrangement in a
production environment for a device that should be as small and light as
possible. Therefore, alignment in two stages is provided. First, the
components of the personal display are coarsely aligned using mechanical
means, and then the fine adjustment of the line-of-sight of each of the
two binocular image sources is aligned to correct for errors in the
θ angle by electronically shifting the image across the image
source in the X direction. Similarly shifts in the Y direction can be
used to adjust errors in the φ direction. There is also a requirement
for aligning the two images in φ which can be achieved by
appropriately rotating the images in the image sources.

[0026]The following numerical example illustrates the significance of the
present invention for a practical personal device. Microdisplays are
commonly used for personal display applications, which are typically
under 25 mm in diagonal. The pixel pitch is typically in the order of 7
to 15 μm. A typical value for the focal length of the imaging lens is
20 mm. Of the different angular tolerances required for binocular
alignment of the angular positions in the θ, φ, and φ
angles, the most critical is often φ with a typical value of a few
minutes of arc, or approximately 1 mrad. An angular tolerance of 1 mrad
with a lens of focal length of 20 mm relates to 20:1/1000=20 μm, which
indicates that the lateral position tolerance of the image source is 20
μm relative to the optical axis of the lens. Such a positioning
tolerance poses a challenge for mechanical alignment in a compact,
lightweight mass-produced structure. In contrast, as this tolerance is of
the same order of magnitude as the pixel pitch of a typical image source,
one could readily move the image by several pixels to center it with
respect to the optical axis of the lens. Thus, only a coarse mechanical
alignment is required. The final, fine adjustments are performed
electronically. Alternatively, should it be possible to manufacture the
mechanical components with sufficient tolerance to meet the coarse
alignment tolerance, only electronic fine alignment would be necessary.

[0027]The present invention is therefore based on a binocular personal
device, which is designed to facilitate binocular alignment. The device
provides the images at infinity, so that parallel image lines-of-sight
are required for good binocular alignment, independent of the eye
position in the system and independent of the content of the displayed
image. This is a simple requirement that is straightforward to calibrate
in production and ensures the personal display remain aligned,
irrespective of the relative location of the eye and the optical axis of
the image. In practice, this also alleviates the need to adjust for IPD
within the allowed eye-motion-box (EMB) of the displayed image. An
electronic method of shifting the image in the image source to perform
the fine angular alignment required for good binocular alignment is also
described. This facilitates and simplifies the design fabrication and
calibration of the lightweight, compact personal display suitable for
mass production.

[0028]Methods to provide the necessary shift of the image on the image
source are considered. Some image sources inherently include electronic
means for shifting the image in the two lateral dimensions. One example
is a CRT image source in which the position of the image within its
screen is controlled by shifting the initial position of the scanning
electron beam. Such image sources can be used for the purpose of the
present invention. The implementation of such image shifts in image
sources, which do not provide this capability built-in, is described
hereinafter. For convenience sake, the discussion will be limited to a
pixel-based microdisplay, such as a transmissive LCD, reflective LCoS, or
self-emitting OLED devices, but it is equally applicable to other image
sources including scanning devices such as MEMs, DLP, or even CRT
devices.

[0029]A method proposed to shift the image laterally is explained with the
aid of the horizontal timing clock sequence of a pixel-based microdisplay
with analog input signals shown in FIG. 3. The sequence describes a
horizontal clock (H CLOCK), which is used to sample the analog signal
scanning across one horizontal image line. The sampled data is entered
sequentially into the line of pixels of the image source, so as to
display the image line. The sequence of each line is initiated with a
horizontal start (H START) signal, itself synchronized to the "new line"
signal (V CLOCK). There are more clock signals per line than pixels in
the image source. In this example, the image source holds 640 pixels but
its control shows 653 clocks. It is therefore quite possible to shift the
beginning of the image line by either suppressing the clocks to begin
with a delay of a few clock periods or adding clock pulses to precede the
first clock. This can be accomplished by adding pipeline delays to delay
the analog signal and similarly delay the clock stream. For example, for
a clock frequency of 20 MHz, an analog delay of 200 ns and no pipeline
delay on the clock stream shifts the image 4 pixels to, say, the left. A
200 ns analog delay and a 4-clock delay to the clock stream generates an
unshifted image line, and, of course, a clock shift of a larger number of
clocks, shifts the image to the right. The same time shift as applied to
the analog signal is also required for the vertical clocks.

[0030]A similar pipeline arrangement is also applicable to shift the image
vertically by shifting the vertical clock. Adding clocks to precede the
first clock will cause skipping of the same number of display lines at,
say, the top of the image. This will shift the image downwards.
Similarly, delaying the first vertical clock by a number of clocks will
load data from a lower line to the top line of the image and effectively
shift the image upwards. In both the horizontal and the vertical shifts
it may be advantageous to electronically force a "zero signal" to
generate "dark pixels", to ensure that the unfilled pixels appear as part
of the image frame.

[0031]An alternative method for modifying the displayed image for the
purpose of fine-tuning the binocular alignment, is shown in FIG. 4. The
display signal is fed by a sequencer 22, alternately to two buffers: odd
signal image frames to buffer 24, and even signal image frames to buffer
26. In analog display signal streams, it is necessary to first convert
the data to digital form, which is effected by an A/D converter 27. While
one buffer is filled up, the other buffer is read by a suitable processor
28 performing modifying operations on the stored image frame, so as to
controllably affect the projection of the image lines-of-sight angles of
each image. The modified image data is then fed to the image source 30 to
display a modified image as necessary to affect the fine adjustment of
the binocular alignment. In analog display signal streams it is necessary
to convert the data back into the required analog form. This
implementation is more flexible than shifting the image clocks as
proposed above, and permits programming to a variety of image modifying
operations, including lateral image shift or image rotation. It may be
advantageous to generate "dark pixels" in display regions that are
"vacated" to ensure that the unfilled pixels appear as part of the image
frame. Additionally, it is foreseen that for certain applications, the
shift of the image may be required with sub-pixel resolution, to which
suitable algorithms are available.

[0032]The present invention also provides means for monitoring the
binocular alignment of the personal display, thereby facilitating
adjustment and calibration. FIGS. 5A to 5D schematically illustrate four
arrangements for monitoring the alignment of a binocular personal
display: a) using a large aperture autocollimator; b) using an
autocollimator and folding optics; c) using folding optics, a magnifying
lens and an imaging device, and d) using folding optics and both an
autocollimator and a magnifying imaging device simultaneously. FIG. 5A
illustrates a sufficiently large operative autocollimator 32 which can
accommodate the input image beams 34, 36 from both sources
simultaneously. Suitable input image patterns are used in each of the
image sources. Here it is appropriate to illuminate only the central
pixel, or small number of pixels central to the image of each image
source, so as to generate essentially a single plane wave in the
direction of the line-of-sight of the virtual image. As the images are
focused at infinity, they each generate fine vertical and horizontal
lines in the autocollimator; misalignment in the θ angle appears as
a separation between the vertical fine lines associated with each image,
whereas misalignment in the φ angle appears as a separation between
the horizontal fine lines associated with each image, as seen the
autocollimator. The image sources, or at least one of the image sources,
should be adjusted to eliminate the separation of the autocollimator fine
lines generated by the left image and the right image, at which point the
personal display is calibrated. Adjustment can be performed both
mechanically by moving components for coarse adjustment, and
electronically, by modifying the images of either image source for fine
adjustment.

[0033]Alternatively, referring to FIG. 5B a small aperture autocollimator
can be used for the same purpose. This requires, in addition, a suitable
optical folding device 38. The optical folding device 38 should be
constructed to ensure that the input angles of both image beams, 34, 36
are reproduced with high accuracy at the output of the optical folding
device 38. This is advantageously achievable with a parallel-sided
rhombic prism or other optics. The main requirement is an accurate
parallelism of the rhombus, ensuring that small tilts and displacements
of the rhombic prism relative to the optical system being tested, are not
significant. Suitable input image patterns are used in each of the image
sources. Here it is also appropriate to illuminate the central pixel, or
small number of pixels central to the image of each image source, so as
to generate essentially a single plane wave in the direction of the
line-of-sight of the virtual image. The operation of the autocollimator
itself, with two fine crossed lines generated by each image, is similar
to the description above for the large aperture autocollimator option.

[0034]Alternatively, an alignment using an imaging device is shown in FIG.
5C. Here folding optics are used to bring the images from either beam 34,
36 into an aperture of a magnifying lens 40. A folding optics device 38,
which ensures accurate reproduction of the angles of the inputs and the
output beams, is introduced to reduce the spread of the two images. The
two images are then projected to an imager 42, e.g., a sensor or a CCD
camera, for viewing, or to be simply viewed by an eye. The image from the
imager 42 can be displayed on a monitor (not shown), or input into a
computer (not shown), for automated analysis. Suitable image patterns are
used in each of the image sources. Here it is appropriate to generate
some form of a grid or a frame pattern that can be used to align the
images relative to each other. When these images overlap, the personal
display is binocularly aligned. Alternatively, it is advantageous to
apply a deliberate safety misalignment in the θ angle inwards, so
that the lines-of-sight of the two images cross. The slight "cross-eye"
condition is convenient to the user and is preferred to an "outward
parallax" condition, which cannot be tolerated. Adjustment is
advantageously performed both mechanically, for coarse adjustment, and
electronically for fine adjustment, by modifying the images of either
image source. Still alternatively, in pixel-based image sources, it is
possible to use the grid pattern of the image source itself as a pattern
suitable for binocular alignment in the imager 42.

[0035]Turning now to FIG. 5D, an alignment using both an imager 42 and an
autocollimator 32 simultaneously, is illustrated. Here, two folding
optics devices 38, 44 are used to bring the images from either beams 34,
36, into either device 38, 44, each operating as described above.
Suitable patterns required for each alignment device, can be generated
separately for implementing the alignment with each device. The advantage
of using both the imager 42 and the autocollimator 32 is the ability to
conveniently align all the necessary binocular parameters in one setup.
The autocollimator 32 is sensitive to misalignment in the θ and
φ angles, but cannot monitor any rotational misalignment in φ
between the two image sources. The imager 42 is capable of monitoring
alignment errors in φ, but is relatively less sensitive to
misalignment in θ and φ as compared to the autocollimator.

[0036]Additionally, and alternatively, any of the embodiments shown in
FIGS. 5A through 5D can be automated. In arrangements deploying an
autocollimator 32 (FIGS. 5A, 5B and 5D), a camera (not shown) is added to
pick up the patterns detected by the autocollimator 32 and feed those
into a processor for display and analysis. Similarly, the image from the
imager 42 (FIGS. 5C and 5D) is input into a processor for display and
analysis. The processor (not shown) is programmed to also generate the
required patterns onto the images sources of the personal display device
under calibration. The processor further controls the electronic image
modifications for fine adjustments, and any automated mechanical controls
provided. The processor can be operative to perform completely automated
binocular alignment procedures.

[0037]FIG. 6 illustrates three embodiments for the folding optics suitable
for the use in the binocular alignment apparatus. FIG. 6A shows a rhombic
prism 46 arrangement. Here, the image intended for the left eye 6 is
reflected off reflector 48 and then off a semi-transparent reflector 50,
and the image intended for the right eye 8, is transmitted straight
through the semi-transparent reflector 50. The propagation directions of
the image intended for the left eye 6 at the input to the prism 46 and
the output from the prism are identical to a tolerance closely resembling
the tolerance of error in parallelism between the reflector 48 and
semi-transparent reflector 50. Furthermore, the output propagation
direction remains parallel to the input propagation direction to the same
tight tolerance irrespective of any angular or linear misalignment of the
prism. Thereby, the images for the left and for the right eye can be
monitored on a relatively small aperture of a detecting device, whether
it is an imager 42, such as a camera (as in FIG. 5C), an autocollimator
32 (as in FIG. 5B), or another device.

[0038]The size and cost of a rhombic prism for typical IPD values (around
64 mm) and having sufficiently large apertures can be large. An
alternative implementation that can reduce the manufacturing cost of the
folding optics is shown schematically in FIG. 6B. Here, two standard
off-the-shelf reflecting components 48, 50 are mounted on a suitable
rigid frame 52. The reflecting component 48 can be implemented with a
beam splitter, a mirror, or a reflecting prism. The semi-transparent
reflecting component 50 is implemented with a beam splitter. Both of
these components are mechanically mounted onto a rigid frame 52 and
aligned to ensure that the reflector and semi-transparent reflector are
parallel to each other to a tight tolerance. The arrangement of FIG. 6B
operates in the same manner as described above for the arrangement of
FIG. 6A.

[0039]An alternative embodiment with a more compact size is shown in FIG.
6C. Here, an LOE 56 serves to fold the image of the left eye 6 onto the
image of the right eye 8. The semi-transparent reflector 50 and reflector
48 are fabricated parallel to each other, so as to ensure that the output
propagation direction is identical to the direction of the input to a
tight tolerance. This arrangement is more compact in that it takes
advantage of total internal reflection in the light-guide to fold the
images propagating between the reflector 48 and semi-transparent
reflector 50. In other respects, the arrangement of FIG. C operates in
the same manner as described above, for the arrangement in FIG. 6A.

[0040]Each of the arrangements in FIGS. 6A, 6B and 6C can be designed to
advantage by ensuring that the intensity of the two images in the eyes 6
and 8 are nearly equal. This is accomplished by equating the
transmissivity of the semi-transparent reflector 50 to the product of
reflectivities of reflector 48 and the semi-transparent reflector 50,
such that T50≈R48×R50.

[0041]FIG. 7A illustrates a typical binocular personal display arrangement
with, in addition to the rigid mechanical body 10, image sources 2 and 4
and lensing devices 12, 14, also two combiners 58, 60. Such combiners are
commonly added for see-through applications, for modifying the
geometrical configurations of the personal display or for compactness
consideration in non-see-through personal displays. Although the addition
of a combiner substantially modifies the mechanical and optical
characteristics of the personal display, in terms of the binocular
alignment process they are treated in the same manner. Here too the
images 16, 18 are located at infinity, and for good binocular alignment
the lines-of-sight of the images should be aligned parallel to each
other. Coarse alignment is performed mechanically; fine alignment is
performed electronically by suitably modifying the images of each image
source as described above. Similar electronic means as described above
for modifying the images are used.

[0042]Of particular interest to the personal binocular device with
combiners 58, 60 is the implementation of LOE-based combiners, as
illustrated in FIG. 7B. Advantages of deploying this structure are as
follows: [0043]a. The overall size of an LOE-based binocular personal
display is significantly smaller than any other implementation for a
given field-of-view (FoV); [0044]b. The LOE facilitates large eye-motion
box (EMB) values without increase in overall system volume. This is of
particular interest for a binocular personal display as, according to the
present invention, the binocular alignment of the personal display is
insensitive to eye movements within the EMB. The EMB can be made
sufficiently large to cover a relatively large IPD range, alleviating the
need for IPD adjustments. Practically, either a single IPD is designed to
cover the entire variation of the population, or a small number of IPD
sizes is devised to cover large ranges of the populations, e.g.,
designing a Small, Medium and Large setting; [0045]c. An LOE-based
binocular personal display can be configured in the "top down"
configuration, as shown in FIGS. 6A to 6C, which is more suitable for
incorporating into head-gear, or in a "side" configuration (see FIG. 8),
more suitable for incorporation into a standard eye-glasses format, and
[0046]d. Other advantages of an LOE-based personal display, include the
inherent see-through capability, the unprecedented compactness of the
combiner in front of the eye, the ability to expand the pupil of the
lensing optics allowing the use of small lensing optics and image sources
even for a large FoV device and high performance of the combiner itself.

[0047]FIG. 8 illustrates an embodiment of the present invention in the
form of a wearable fixture, e.g., eyeglasses. A rigid frame 62 holds two
LOE combiners 58, 60. Two image delivery pods 64, 66 are also mounted
onto the same frame, one pod 64 for delivery of an image to the left eye
and the second pod 66 for delivery of an image to the right eye. Each pod
is secured with a spherical mount 68 that, when fixing screws 70 are
released, allows mechanical angular tilting of each pod. Once in the
correct orientation, the pods are secured in place by tightening the
screws 70 in that position. This mechanism serves for affecting coarse
adjustment for binocular alignment of the device. Here the two pods are
angularly tilted in three axes θ, φ and φ to reach the
correct alignment position with respect to each other. This
implementation takes advantage of the following features of the device:
[0048]a. The direction of propagation of the images is essentially
independent of the linear positions of the pods, i.e., the images are at
infinity and the resulting image components are essentially plane waves,
which are not sensitive to lateral (in the X, Y axes) or axial motion (in
the Z-axis); [0049]b. The location of the LOE combiners 58, 60 do not
affect the binocular alignment between the pods. As the image is at
infinity, linear motion of the LOE does not influence the images.
Furthermore, as the reflectors of the LOE combiners are parallel to a
tight tolerance, angular misalignment of either LOE combiners does not
affect the binocular alignment of the overall device. Hence only the pods
need to be aligned relative to each other, and [0050]c. Since the device
is designed to be imaged to infinity, it remains aligned independent of
the content displayed and independent of the location of the eye for as
long as the eyes are located within the EMB. The LOE combiners can be
designed to support a very large EMB, so the same device can fit a large
range of IPDs.

[0051]Instead of using a mechanically adjustable fixture for tilting the
pods to coarse adjustment of the binocular alignment, it is possible to
mount the pods loosely onto the frame. In this solution, the pods are
free to tilt into the desired coarse alignment using external
manipulators, and once in position, the pods are cemented in place.

[0052]An alternative to performing the coarse adjustment of the binocular
alignment mechanically by tilting the pods 58, 60 one relative to the
other, is to fix the pods 58, 60 to frame 62 and mechanically move the
image sources 2, 4 in the lateral directions. A mechanical mount suitable
for such an implementation is shown schematically in FIG. 9. The mount
includes a base formed by a two-part wedge-shaped elements 72, 74 and a
lateral sliding plate 76. The two wedge-shaped elements 72, 74 serve to
adjust the axial separation between the image sources 2, 4 and the
lensing devices 12, 14 (not shown), while maintaining the image sources
2, 4 perpendicular to the optical axis of the lensing devices 12, 14,
respectively. The image sources 2, 4 are mounted onto the lateral sliding
plate 76. The lateral sliding plate 76 is mounted in an accurate axial
position when placed against the top surface of the elements 72, 74. The
sliding plates 76, however, are free to translate laterally by means of
locating grooves 78 which are larger than the locating pins 80. Once the
focal distance of the image source is set through adjustment of the
relative positions of the wedge-shaped elements 72, 74, lateral
manipulators (not shown) grip the sliding plate 76 in its gripping
grooves 82 and adjusts its lateral position with respect to the lensing
elements. The sliding plate 76 is then affixed, e.g., cemented into
position, so as to set the correct binocular alignment of the overall
device.

[0053]A further optional feature of the embodiments of the present
invention is the incorporation of ophthalmic corrective lenses. A main
attribute of the present invention is the focus at infinity. In order to
accommodate myopic users, it is necessary to allow correction of the
user's vision for comfortable viewing of images at infinity. In the "top
down" configurations shown schematically in FIGS. 7A and 7B, this is
solved by mounting the personal display device over any user-worn
ophthalmic eyeglasses. In the eyeglasses embodiment shown in FIG. 9,
however, it is preferable to incorporate such ophthalmic correction
within the same device. This can be accomplished by mounting suitable
ophthalmic corrective lenses onto the same frame, between the viewer's
eyes and the LOE-combiners. These can be mounted onto the same frame, on
a separate clip-on frame mounted internally, or onto the LOE's
themselves. A further modification for the convenience of the user
relates to means for reducing the external brightness when using the
device in a see-through mode. Here it is possible to mount a partially
transmitting filter in front of the LOEs (between the LOE and the virtual
image) or paint the front surface of the LOE, or add an active filter
with photo-chromic, or electronic control of the transmissivity.

[0054]It will be evident to those skilled in the art that the invention is
not limited to the details of the foregoing illustrated embodiments and
that the present invention may be embodied in other specific forms
without departing from the spirit or essential attributes thereof. The
present embodiments are therefore to be considered in all respects as
illustrative and not restrictive, the scope of the invention being
indicated by the appended claims rather than by the foregoing
description, and all changes which come within the meaning and range of
equivalency of the claims are therefore intended to be embraced therein.